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Sci Rep. 2018 Jan 31;8(1):1991. doi: 10.1038/s41598-018-20494-y.

Black silicon significantly enhances phosphorus diffusion gettering.

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Aalto University, Department of Electronics and Nanoengineering, Espoo, 02150, Finland.
Aalto University, Department of Electronics and Nanoengineering, Espoo, 02150, Finland.
Fraunhofer Institute for Solar Energy Systems, Freiburg, 79110, Germany.
University of Freiburg, Department of Sustainable Systems Engineering, Freiburg, 79110, Germany.


Black silicon (b-Si) is currently being adopted by several fields of technology, and its potential has already been demonstrated in various applications. We show here that the increased surface area of b-Si, which has generally been considered as a drawback e.g. in applications that require efficient surface passivation, can be used as an advantage: it enhances gettering of deleterious metal impurities. We demonstrate experimentally that interstitial iron concentration in intentionally contaminated silicon wafers reduces from 1.7 × 1013 cm-3 to less than 1010 cm-3 via b-Si gettering coupled with phosphorus diffusion from a POCl3 source. Simultaneously, the minority carrier lifetime increases from less than 2 μs of a contaminated wafer to more than 1.5 ms. A series of different low temperature anneals suggests segregation into the phosphorus-doped layer to be the main gettering mechanism, a notion which paves the way of adopting these results into predictive process simulators. This conclusion is supported by simulations which show that the b-Si needles are entirely heavily-doped with phosphorus after a typical POCl3 diffusion process, promoting iron segregation. Potential benefits of enhanced gettering by b-Si include the possibility to use lower quality silicon in high-efficiency photovoltaic devices.

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